1. Field of the Invention
The present invention relates to a negative-angle press-working die, which performs bending or the like of an automobile panel with negative angle working.
2. Prior Art
Negative angle working to be performed on a front pillar, roof and rear window of a body side outer panel of an automobile panel is difficult as the front pillar, roof and rear window have complicated cross-sectional shapes. Because the cross-sectional shape of a portion from the front pillar to the roof needs to keep the strength with a small cross section, negative angle forming of this part is particularly difficult. As a press-working die to overcome such difficulty, a press-working die disclosed in, for example, JP-A-59-197318 is known. As shown in FIG. 8A, the press-working die is of a columnar cam type that includes a lower die having a hold part 16b for holding a raw material on the upper portion of a fixed punch 16a of the lower die, and a cam groove having an arc surface continual to the hold part 16b, a columnar rotary cam 17 which is provided at the lower die 14 to be rotatably inserted in the cam groove and has a bending part 17a at its one end, an elevatable and laterally slidable aerial cam which is provided above the rotary cam 17, has a bending blade at a distal end, and rotates the rotary cam 17 in a direction of holding the raw material, and a pad elevatably disposed above the hold part 16b of the lower die. The press-working die performs complicated bending of the pillar (workpiece 12) with the rotary cam 17.
Recently, the demanded cross-sectional shape of a workpiece is getting complicated, for example, from the one shown in FIG. 8A to the one shown in FIG. 8B, so that even the use of the conventional negative-angle press-working die makes it difficult to achieve negative angle forming. That is, as shown in FIG. 8B, the shape is thin and has deep bending, so that the width where the fixed punch 16a or hold part is present cannot be set, and with a clearance 18 for panel removal provided, the space becomes larger, so that the raw material panel cannot be pressed with the pad of the upper die. This leads to reduction in the quality of the formed panel. If the bending of the curved shape of a workpiece is deep and the level difference in the up and down direction is large, the separation line between the fixing punch and the rotary cam has different heights at individual cross sections, and designing the panel with a single cross section is not possible. It is therefore necessary to separate the press-working steps, or separate a die 20 of the columnar cam type into a front pillar A, roofs B, C, a rear D, and so forth, as shown in FIG. 9, which need to be arranged along the inclinations of the respective workpiece and need to be formed in multiple steps.